Manufacture of sulphite paper pulp



Sept. 15,

means ALFRED m. rnoaisuu, or sen Francisco. cazcrroan'la MANUFACTURE OFSULPHITE IEAPER ZP'UI'P 35o Drawing.

It has long'been known that acid sodium sulph-ite is a far bettercooking medium than the corresponding salts of either limeor magnesia ormixtures of both, and were it not for the greater cost it would beforethis have become the recognized standard. Many suggestions have beenmade to overcome this difficulty by rendering the operation cyclic sofar as the soda is concerned, soda and sulphate cooking being taken aspatterns. But

these recovery systems cannot be said to solve the problem. There isstill quite a loss of soda and impurities gradually build up in thecircuit causing much trouble. 4

Hereinafter, I use the phrase reducing conditions in the sense of ageneral term, customarily employed by those familiar with the art, todesignate some type or form of chemical changegconducted in the absenceof oxygen, or with insufficient oxygen for complete combustion.

The new and useful improvement which I have invented overcomes all thisdifficulty, uses a cheap source oi soda as raw material,

and yields as an end product another salable soda compound worth many"times the cost of the raw material employed. It is not quite correct toconsider this compound merely as a by-product of the pulp industry. Therelative values are such that it is more correct to say that the processis undertaken to manufacture two major products, e. g, paper pulp andsodium sulphide.

The process consists of the following steps:

(1) Manufacturing sodium bisulphite by decomposing the ordinary limecooking liquor with sodium sulphate, and removing the calcium sulphateformed.

(11) {looking the wood with this liquor and separating the pulp from thespent waste liquor as in ordinary practice.

Neutralizing this spent liquor with sodium carbonate produced later inthe proc see under (V1), and adding sulficient excess to remove thecalcium sulphate not separated under (3), separating the calciumcarbonatethus formed.

(IV, Evaporating the liquid from (Ill) in multiple effect evaporatorsuntil of a syrupy consistency.

Application filed March 25,

1929. Serial No. 349,897.

(V) Incinerati-ng said syrupy liquor under reducing conditions wherebyan ash consisting principally of sodium carbonate and sodium sulphide isobtained, and all organic matter removed.

(VI) Dissolving the ash from (V) in water and separating the two majorconstituents of same by fractional crystallization. .1

(VII) Returning the carbonate recovered in (VI) to the circuit under(111) and packing the sulphide for sale.

Necessarily, these steps can also be applied to the waste liquor of theordinary sulphite process, rendering its disposal remunerative Wherevercheap saltcake is avaiable. The steps therefore become altered asfollows: i

(I) Neutralizing the waste liquor with sodium carbonate.

Adding sodium sulphate and separating the resultant calcium sulphatesludge.

(Ill) Adding excess sodium carbonate and separating the calciumcarbonate precipitated.

(IV) Evaporating the liquid from (111) to a. syrupy consistency inmultiple cliect evaporators. 1

(V) lncinerating said syrupy liquor under W reducing conditions wherebyas ash consisting principally of sodium carbonate and sodium sulphide isobtained, and all organic matter destroyed.

(V1) Dissolving the ash from (V) in wa ter, and separating the two majorCOllStltll cuts of same by fractional crystallization.

(VII) Returning the carbonate recovered in (Vi) to the circuit under (I)and (HI),' and packing the sulphide for sale.

In both these instances the cost of paper pulp has been much reduced bythe simultaneous production of another valuable prod not; a nuisance inthe shape of waste liquor has been disposed of and turned into a profit,

and in the first instance cited a superior grade of pulp has likewisebeen produced.

I claim: I

1. In the process of manufacturing paper pulp the method consisting ofdecomposing an acid calcium sulphite solution with sodium sulphate,separating the calcium sulphate produced, digesting the chips with theliquor thus produced, separating the pulp from the spent liquor,neutralizing said liquor and removing calcium sulphate from same ascalcium carbonate by" means of sodium carbon ate, separating the sludgeof calcium carbonate formed, evaporating the liquor thus obtained to asyrupy consistency, incinerating said liquor under reducing conditions,dissolving the resultant ash in Water, separating the contained sodiumcarbonate from sodium sulphide, and. returning the sodium carbonate tothe process for neutralizing the above-mentioned liquor. 2. 1n theprocess of manufacturing paper 7 pulp, the method consisting of cookingthe chips with an acid solution of calcium bisulphite, separating thepulp from the spent liquor, neutralizing said liquor with sodiumcarbonate, adding saltcake to precipitate cal- 'cium sulphate, removingthe calcium sulphatc, adding sodium carbonate to the result ing liquorand removing the calcium 'carbonate "produced, evaporating the liquor toa syrupy consistency, incinerating said syrupy the resultant ash inWater, separating the conllquorunder reducing conditions, dissolvingtained sodium carbonate from sodium sulphide, and returning the sodiumcarbonate to the process for neutralizing-the above-mentioned liquor.

In testimony whereof I hereunto-set my signature.

' ALFRED M. THOMSEN.

